My first firewall was a Thinkpad 750Cs. ;) I can't recall the distro I was running at the time - likely Debian or Slackware. At one point I returned from vacation to find that the hard drive had failed a couple days earlier. Since the firewalling was in the kernel, all I lost was logging. IIRC the last log message was that it was remounting the root filesystem readonly. It continued operating for a couple more weeks until I could arrange to replace it.